The invention relates to a safety belt retractor as a safety system in motor vehicles with, as a carrier of the belt strap wound thereon, a belt shaft mounted in a U-shaped housing, and with, as a force limiting element, a rotation dampener that acts upon the belt shaft.
A safety belt retractor having the aforementioned features is described in GB-PS 1 440 232. In this connection, there is disposed in the interior of the hollow shaft body of the belt shaft a piston that is axially displaceable upon a threaded rod and that at an end face is introducible into a working space that is filled with a highly viscous medium, and in its axial longitudinal direction is provided with transfer channels via which the medium that is displaced out of the working space and during introduction of the piston can flow off. The piston is coupled with the shaft body, while the threaded rod is connected with the blocking system of the belt retractor. Therefore, if during locking of the belt retractor a further tensioning of the belt strap occurs, and a rotation of the shaft body connected therewith, the piston is axially displaced upon the threaded rod, and the desired force limitation is thus effected via the displacement of the medium out of the working space.
The known rotation dampener has the drawback that the introduction of the viscous medium into the rotation dampener, as well as the sealing of the receiving chamber in the interior of the belt shaft are difficult, and it is therefore an object of the present invention to provide a rotation dampener for a safety belt retractor of the initially mentioned type that has a simplified construction, even as an independent subassembly that can be pre-assembled.
The realization of this object, including advantageous embodiments and further developments of the invention, result from the content of the patent claims that follow this description.
The basic concept of the invention is that the rotation dampener comprises a cylindrical housing that is filled with a highly viscous medium and that has at least one apertured disk fixedly disposed therein, and in the housing, parallel to the apertured disk, is disposed a disk piston that is fixedly connected with the belt shaft, the rotation of which is to be dampened, and that has a radially extending piston wing that rotates upon rotation of the disk piston. The invention has the advantage that during the rotation of the disk piston relative to the apertured disk there is no displacement or overflow of the medium, but rather that the shearing forces that result between the two disks (apertured disk and disk piston) that rotate relative to one another are utilized for the force limitation.
As one exemplary embodiment for the utilization of an inventive rotation dampener in a safety belt retractor, the invention is initially directed to flanging the housing laterally on the housing of the safety belt retractor, with the disk piston being connected to the belt shaft. To the extent that such a safety belt retractor already has a force limiting device in the form of a torsion rod that is connected with the belt shaft, it can be provided that the disk piston be connected with the torsion rod as an additional force limiting element.
Alternatively, the rotation dampener can be integrated into the shaft body of the belt shaft, which shaft body is for this purpose hollow, whereby in the shaft body, as a carrier of the apertured disk that is interlockingly disposed thereon, there is disposed a shaft core that is locked when the safety belt retractor is blocked, and the disk piston is connected to the shaft body via an interlocking connection.
Pursuant to specific embodiments of the invention, a plurality of disk pistons and apertured disks can be provided in an alternating arrangement, and/or a respective spacer disk can be disposed between disk pistons and apertured disks.
A silicone is preferably used as highly viscous medium. For the general increase of the force level of the force limiter, and to compensate for a possible drop in force at higher temperatures, it can be provided that the silicone is already under increased pressure prior to the activation of the force limitation. This can be brought about by filling the silicone into the housing at an appropriately high pressure.